Executive producer Roberto Aguirre-Sacasa told EW that Sabrina is likely to show up in Riverdale since the character is part of the Archie Comics universe:

Some people don’t even know that Sabrina is in the Archie family. There is absolutely a universe where Sabrina pops up in Riverdale or one town over in Greendale. Certainly, the priority is launching Riverdale and making sure that show is as good as it can be and as embraced as we want it to be.”

Melissa Joan Hart of course played the famed witch in her own TV show, Sabrina the Teenage Witch, which ran on ABC between 1996 and 2000 and on The WB until 2003. While Hart may not reprise the role, Aguirre-Sacasa said Sabrina will almost certainly make an appearance: